eUrasia Power has provided a glossary of power conversion and related industry terminology. Click on a link below to get a definition of a power supply or related term. Hint: After clicking the drop down dialog box, enter the first letter of the term you are searching for, e.g. “P” for Power Factor Correction

Electrical current that continuously reverses direction of flow , typically in a periodic fashion . In the United States , standard AC power sources reverse direction sixty times each second (called 60 cycles or 60 Hertz AC ) . In Europe , the standard is 50 Hertz. Aerospace applications require 400 Hertz.

Also known as convection cooling. Applies to designs that dissipate heat without the use of fans or cooling liquids . Air cooled devices often rely on a heat sink to enhance heat dissipation.

Unit of measure of current flow. At any given point in a circuit an Amp (1A) equals 1 coulomb of electrons passing in 1 second.

The Intel® ATX specification defines the form, fit and functionality of a power supply intended to be used with ATX motherboards. This specification is an evolution of the Baby-AT form-factor. The major differences between ATX and the PS/2 (Baby-AT) is the addition of a 3.3V rail, Voltage standby (Vsb), PS On signal, and a twenty pin connector vs. two six pin connectors. The size of the ATX form factor is 5.91 x 3.39 x 5.51 inches / 150 x 86 x 140 mm.

This new version of the Intel� ATX power supply is comprised of a standard ATX unit plus the following enhancements: Increased +12 VDC output capability and a 4-pin connector providing two 12V pins and two ground pins. The 4-pin connector is intended to power the DC/DC converters on the motherboard.

A cooling fan with a center hub that glides on precision steel balls. Though more expensive, ball-bearing fans typically last longer than fans made with sleeve bushings but are also sometimes louder.

The range of frequencies over which something is measured.

The insulation applied to live parts to provide basic protection against electric shock. May exclude insulation used exclusively for functional purposes.

A power supply system where if the AC line fails, a battery will provide input energy to keep the DC outputs from failing

Statistically, if an electrical device is going to fail, it will most often occur during its first hours of operation. Some suppliers first operate new electrical products at their factory for a predetermined period to weed out problems before shipment to customers. This process, known as burn-in, is conducted with the product under electrical or thermal load, to induce stress and make it easier to identify potential failures.

A Canadian safety agency that establishes standards and tests products for public safety

Measured in farads, capacitance is an object ability to store a charge

An electronic component that can store an electrical charge on conductive plates. For power supplies it is best to use capacitors with a low ESR (equivalent series resistance), and high temperature rating (i.e. 105 degrees C).

The component of EMI noise that is common to both the DC output and return lines with respect to input neutral

The component of noise that is common to both the DC output and return lines with respect to input neutral.

A power supply which is designed to regulate its output current within a specified range and compensate for changes in AC input(line), load, ambient temperature and time.

A power supply which is designed to regulate its output voltage within a specified range and compensate for changes in AC input(line), load, ambient temperature and time.

The circuitry in a closed loop system which maintains the control loop by incorporating an error amplifier in the feedback of the system.

Also known as air cooling. Applies to designs that dissipate heat without the use of fans or cooling liquids . Air cooled devices often rely on a heat sink to enhance heat dissipation.

A unit of electric charge equal to the quantity of electricity transferred by a current of one ampere in one second

In a multiple output power supply, the percent voltage change at one output caused by a load change on another output.

A method of overvoltage protection which rapidly places a low resistance shunt across the power supply output terminals if a predetermined voltage is exceeded.

Represented by the symbol I, current is the flow of electrons through a material. Current is measured in amperes.

A control circuit within a power supply that limits the amount of the output current to prevent damage to the power supply and the equipment in which it is being used. There are two common current limit methods. The most predominate type is the foldback current limit where the voltage and current decline simultaneously once a predetermined point is reached. The other type is block wall current limit where the voltage and current quickly go to zero once a predetermined threshold is reached.

The number of times an alternating current reverses in one second measured in hertz (Hz)

A logarithmic measure of signal power determined by comparing an initial reference level to a final measurement

A reduction in the of amount of output power that can be drawn from the power supply due to increased ambient temperature. Often a power supply company will give a derating specification, i.e. derate linearly to 50% output power at 70 degrees C.

The component of noise measured between DC output and output return. This is typically how “ripple and noise” specifications are measured.

Electrical current that flows only in one direction.

Distributed power system architecture is one where the point of regulation is distributed to the point of use. This distribution includes a bulk voltage that is distributed to the DC-DC converters local to the points of use (loads).

Additional insulation applied to basic insulation in order to reduce the risk of electric shock in the event of a failure of the basic insulation.

The change in power supply output over a specified period following a warm-up period when all other characteristics such as line load and ambient temperature are constant.

The ratio of output power to input power to measure the efficiency of an AC-DC power supply. Efficiency is typically measured at full load and nominal input voltage

The equivalent series resistance (e.s.r.) is made up of several resistive components within the capacitor , including electrolyte, tissue separators, foils etc.

The method of limiting the output current by reducing both the output current and voltage simultaneously.

High Potential Testing, or Hi-Pot, is a dielectric withstanding voltage test. The intent of this test is to verify the discontinuity between circuits and locate material defects within a product. This test is performed by creating a high voltage potential between two circuits. Hi-Pot testing can find defects that a conventional continuity test will not find, such as high resistance shorts and unintentionally tight copper-to-copper spacing.

The amount of time that the output voltages will maintain regulation after loss of AC power. Typically on switch mode power supplies the hold up time will be 20 milliseconds or slightly greater then on AC cycle.

The amount of AC input current drawn from the power supply when first turned on. The AC input current reduces to a lower steady-state current once the input bulk capacitors are charged.

Just a Bunch of Disks

AC or DC current flowing from the input to the output or chassis of an isolated power supply at a specified voltage.

The percentage of change in output voltage due to a change in the input voltage. This is usually measured by varying the input voltage from low line high line.

The percentage of change in output voltage due to a change in output loading. This is usually measured by varying the load applied to the power supply from no load to full load.

The amount of DC current which must be drawn from an output of the power supply to maintain regulation

MTBF is a method used to estimate reliability. MTBF may be calculated and/or demonstrated. Calculated MTBF values are either based upon Mil HDBK 217 or the BELLCORE Issue 4 and Issue 5 using the parts count method. Demonstrated MTBF is based on Life Testing and Ongoing Reliability Testing (ORT) using monitored burn-in and reported field return information..

The sum of all output wattages (volts * amps) expressed in watts. Power supplies have a both a continuous rating and a peak rating. The output power can vary depending on the ambient temperature.

A power supply protection circuit which prevent excessive voltage coming out of the power supply from damaging the system. OVP is triggered when the power supply output voltages exceed a pre-determined value

PARD is a term used for the sum of all ripple and noise components measured over a specified band width and stated in either peak-to-peak or RMS values.

Peak current is defined as the extra amount of DC current over the nominal output rating that the power supply is capable of generating for brief periods ot time.

PFC is the ratio of true input power to the apparent power (rms voltage x rms current) in AC circuits. This power is generally considered to be wasted, but can be corrected for. Switching power supplies draw input current in short, high-magnitude pulses. These pulses can be smoothed out over the input voltage cycle by using “active” or “passive” techniques. The use of power-factor correction significantly reduces these high peak currents and makes the supply appear as a linear load to the power system. The ideal Power Factor is unity (1.0). However, Power Factor can range from anywhere between 0 and 1.

n electronic signal generated by the power supply which warns of impending power failure.

A signal coming from the power supply, usually TTL high, which indicates that the output voltage is within its specified regulation levels.

RAID is an acronym for Redundant Array of Inexpensive Disks. RAID technology allows data to be spread across multiple physical drives (called an “array”). This data-distribution technique, known as “striping”, complements the way the operating system requests data, and can offer improved performance and reliability.

Data is written on stripes across all drives in the array. Performance is increased, however this level does not allow for any data redundancy. If one drive is lost all data is lost. Total array capacity increases with each drive. For optimal performance, all drives in the array should be the same size.

Data protection through redundancy. Data is mirrored on the second hard drive of the same capacity. This process slows performance. Requires two drives of the same capacity.

This RAID level is no longer used.

This level uses the byte level striping technique. Is not commonly used

Data is written using a striping technique which writes data across all drives in the array except the one which receives the parity at the block level. Data can be restored if any single drive fails. Capacity of the array is all drives less the parity drive.

Data and parity is written across all hard drives in the array unlike the parity drive used in Level 4. Data can be restored if any single drive fails. Data capacity is all drives less one drive due to the parity information.

Power supplies connected in parallel operation so that if one fails, the others will continue delivering enough current to supply the maximum load. This method is used in applications where power supply failure cannot be tolerated.

The ability to connect power supplies in parallel so that if one fails, the other power supply will electronically switch on line and provide continual power to the load. The mode is used when power supply failure cannot be tolerated.

Remote Sense – Detection of output voltage at a load remote from the power supply, enabling the power supply to regulate output voltage and to compensate for voltage drop across power cables. Permits greater accuracy of regulation than local sensing.

The AC component on the DC output of a power supply usually expressed in millivolts peak-to-peak or RMS and measured over a 20MHz bandwidth

A feature which limits the output current of a power supply under short-circuit conditions so that the supply will not be damaged.

The frequency at which the pulse-width modulator switches the bulk DC voltage in a switching power supply.

A ratio by which the changes in power supply output voltage caused by temperature changes can be calculated. Usually output decreases as ambient temperature rises.

The average change in output voltage regulation expressed as a percentage per degree centigrade ambient temperature change.

An internal safeguard circuit in a power supply which shuts down the unit in the event of excessive internal temperature.

Time required for output voltage to return to regulated value after a step change of output current, usually specified in microseconds for a specified percentage of load change.

Power supply`s ability to accept a wide input voltage range (90VAC to 264VAC) without the selection of input range, either manually or electronically (as in autoranging input).

The temperature of the environment in which the power supply is operating, usually specificed in degrees Centigrade, e.g. 50 degreeA standard used to measure the diameter of a wire conductor. The greater the number, the smaller the wire diameter. House wiring typically contains 12-gauge or 14-gauge solid wire. Power supply cables typically use 18~20 AWG wire. Digital circuit boards are sometimes modified using small 22-gauge or 28-gauge wires.

The temperature of the environment in which the power supply is operating, usually specificed in degrees Centigrade, e.g. 50 degrees C